Bunghole banter

In a heated discussion a student recently told another student to "Stick it in your bunghole!"

When I asked him if he was aware of what a "bunghole" was, he said he was not, but that it was synonymous with a**hole, and as such was in common usage among young people.

I realize that Rap, Hip-Hop and Pop Culture are notorious for taking established words and phrases and ascribing new meanings to them, but at what point in the evolution of the language do these new meanings become acceptable? Also, I have two requests.

Can anyone provide another example of a word or phrase that started out meaning one thing and ended up meaning something else, and has anyone heard "bunghole" as another term for the double bull in darts?